1. Field of the Invention
The invention relates to the field of communications between terminal via communications networks, and more particularly it relates to ensuring continuity of service for calls that involve networks of different types.
2. Brief Description of the Related Art
A call is often set up between two remote terminals via a plurality of communications networks that are connected to one another via edge routers or border routers. Setting up a call in this way generally presents no problem so long as the call is not associated with some particular level of service, or so long as continuity of service is not required in association with the call. However, this continuity of service situation is becoming less and less frequent because of the great variety of networks and network equipments.
Amongst the network equipment commonly in use and likely to coexist within a single call, mention can be made in particular of IP routers, routers with wavelength-division multiplexing such as dense wavelength-division multiplex (DWDM) devices, add-drop multiplexers (ADMs), photonic cross-connects (PXCs), or optical cross-connects (OXCs).
Similarly, amongst the networks commonly in use and likely to be involved in a call, mention can be made in particular of those which belong to the first family of networks known as “packet switching” networks and those belonging to the second family of networks known as “non-packing switching” networks.
The networks of the first family make use of protocols at level 3 in the open systems interconnection (OSI) layer model (also known as IP level protocols, or more simply Internet protocols (or IPs)). These constitute that which is commonly called the Internet.
Networks of the second family make use of protocols at level 2 in the OSI layer model (also known as sub-IP level protocol). The second family can also be subdivided into at least three sub-families. A first sub-family is constituted by networks using space-division switching, a second sub-family is constituted by networks using time-division multiplexing (TDM), as for example the synchronous optical network (SONET) and the synchronous digital hierarchy (SDH) network, and a third subfamily is constituted by networks using wavelength-division multiplexing (WDM).
In order to enable calls to be set up via different IP networks (belonging to the first family), proposals have been made to connect each network management system (NMS) which manages the equipment of an IP network to apparatus for controlling network level admission. On receiving a request to transfer, via its own network, a call associated with at least one service criterion and specifying another IP network connected to its own IP network, such control apparatus serves to verify whether there are available resources that are capable of satisfying the service criterion(a) associated with the call to be transferred. Thus, so long as such resources exist, the control apparatus can in turn forward the call transfer request to the control apparatus connected to the network management system managing the equipment of the designated IP network, so as to enable it to perform optional verification within its own IP network.
The term “request to transfer a call via a network” is used herein to designate the fact of using a first network to establish a “bridge” between two other networks, making available certain resources of one of the links within the first network.
By means of this type of control apparatus, it is thus possible to guarantee the continuity and the quality of service associated with a call when the IP networks involved in the call are different. However, it is also possible to guarantee security of service to a subscriber, where security of service consists in authenticating and/or encrypting a call.
However, there does not exist any known solution enabling continuity and quality of service to be guaranteed together with optional security of service associated within a single call when the call is set up over networks of different types, i.e. belonging to different sub-families of the second family (known as the sub-IP family) or belonging to different families.
An object of the invention is thus to remedy that drawback.